Constructing an artificial boundary to regulate solid electrolyte interface formation and synergistically enhance stability of nano-Si anodes.

Low coulombic efficiency and poor cyclic stability are two common problems for silicon anodes. Therefore, it is of great significance to improve cycling performance and initial coulombic efficiency (ICE) via rational surface engineering on nano-Si anodes. Herein, a new nano-silicon anode is obtained by straightforward constructing a multifunctional polypyrrole protective layer on the surface of silicon nanoparticles, which is further used as the inner boundary of solid electrolyte interface (SEI) film. Specifically, the Li salt decomposition reaction between the electrolyte and silicon surface is effectively inhibited under the protection of the compact artificial boundary. The transfer of Li for forming the SEI film is selectively slower than that of lithiation/delithiation reaction. This further reduces the amount of SEI film, leading to a high ICE of 93.2% at 0.5 A g for modified nano-Si anodes. In addition, the flexible SEI precursor combined with the high proportion of organic components in SEIs not only accommodates the volume change of nano-silicon, but also suppresses accumulation of "waste SEI", so the electrode can maintain a reversible capacity of 1153.2 mAh g at 1 A g after 500 cycles. This work provides important guidance for surface structural optimization of alloy-type anodes with high volume change.